System and method for repairing high-temperature gas turbine components

ABSTRACT

A method of repairing a component includes removing a damaged portion from the component to leave a first interface surface that is defined by a continuous curve, mixing a powdered base material and a binder to define a mixture, and printing the mixture into a desired shape without melting the base material. The method also includes removing the binder from the desired shape, solid-state sintering the desired shape to form a replacement piece having a second interface surface that is defined by the continuous curve, and attaching the second interface surface to the first interface surface to replace the damaged portion of the component.

TECHNICAL FIELD

The present disclosure is directed, in general, to a system and methodfor repairing high-temperature gas turbine components, and morespecifically to such a system and method for the repair of gas turbineblades and vanes.

BACKGROUND

The difficulties associated with the additive manufacture (AM) ofnickel-base gas turbine components with high gamma prime content makesthe process unsuitable for large scale manufacturing or repair. Inparticular, attempts to additively manufacture components using Alloy(CM) 247, or to repair such components often result in grain boundarymelting and cracking. Alternatively, the components are repaired withanother inferior nickel base alloy that is less prone to cracking,resulting in poor performance of the component.

SUMMARY

A method of forming a component includes mixing a powdered base materialand a binder to define a mixture, forming the mixture into a desiredshape without melting the base material, removing the binder from thedesired shape to define a skeleton, the volume of the skeleton beingbetween 80 percent and 95 percent base material, and infiltrating theskeleton with a melting point depressant material to define a finishedcomponent, the finished component having less than 1 percent porosity byvolume.

In another construction, a component includes a skeleton formed from abase material and defining the final shape of the component, theskeleton having a porosity between 5 percent and 20 percent, and amelting point depressant material disposed within the skeleton, themelting point depressant material filling the pores within the skeletonto define a finished component having less than 1 percent porosity byvolume.

In another arrangement, a method of repairing a component includesremoving a damaged portion from the component to leave a first interfacesurface that is defined by a continuous curve, mixing a powdered basematerial and a binder to define a mixture, and printing the mixture intoa desired shape without melting the base material. The method alsoincludes removing the binder from the desired shape, solid-statesintering the desired shape to form a replacement piece having a secondinterface surface that is defined by the continuous curve, and attachingthe second interface surface to the first interface surface to replacethe damaged portion of the component.

In another construction, a method of repairing a component includesremoving a damaged portion from the component to leave a first interfacesurface, mixing a powdered base material and a binder to define amixture, and micro-injecting a layer of the mixture having a thicknessbetween 10 microns and 100 microns. The method also includes repeatingthe micro-injecting process to form additional layers and complete areplacement piece, heating the replacement piece to remove the binder,sintering the replacement piece, and fixedly attaching the replacementpiece to the component to replace the damaged portion.

In another construction, a replacement assembly for replacing a damagedportion of a component includes a replacement piece including a firstplurality of layers with each layer of the first plurality of layersformed on top of a prior formed layer of the first plurality of layers,the first plurality of layers arranged to define a curved leading edgeportion and a first interface surface, the interface surface defined bya first continuous curve. An attachment piece includes a secondplurality of layers with each layer of the second plurality of layersformed on top of a prior formed layer of the second plurality of layers,the attachment piece arranged to fit between the first interface surfaceand the component to fixedly attach the replacement piece to thecomponent to replace the damaged portion.

The foregoing has outlined rather broadly the technical features of thepresent disclosure so that those skilled in the art may betterunderstand the detailed description that follows. Additional featuresand advantages of the disclosure will be described hereinafter that formthe subject of the claims. Those skilled in the art will appreciate thatthey may readily use the conception and the specific embodimentsdisclosed as a basis for modifying or designing other structures forcarrying out the same purposes of the present disclosure. Those skilledin the art will also realize that such equivalent constructions do notdepart from the spirit and scope of the disclosure in its broadest form.

Also, before undertaking the Detailed Description below, it should beunderstood that various definitions for certain words and phrases areprovided throughout this specification and those of ordinary skill inthe art will understand that such definitions apply in many, if notmost, instances to prior as well as future uses of such defined wordsand phrases. While some terms may include a wide variety of embodiments,the appended claims may expressly limit these terms to specificembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section view of a gas turbine engine.

FIG. 2 is a perspective view of several vanes of the gas turbine engineof FIG. 1.

FIG. 3 is a perspective view an insert piece for use in repairing aturbine vane of FIG. 2.

FIG. 4 is a perspective view of the vanes of FIG. 2 with the insertpiece of FIG. 3 being installed.

FIG. 5 is a perspective view of a component 3D printed to a near netshape.

FIG. 6 is a perspective view of the component skeleton after removal ofa binder and sintering.

FIG. 7 is a perspective view of the component skeleton during aninfiltration of a melting point depressant.

FIG. 8 is a perspective view of the completed near net shape componentfollowing infiltration.

FIG. 9 is a perspective view of another component 3D printed to a nearnet shape.

FIG. 10 is a perspective view of the component skeleton of FIG. 9 afterremoval of a binder and sintering.

FIG. 11 is a perspective view of the component skeleton of FIG. 9 duringan infiltration of a melting point depressant.

FIG. 12 is a perspective view of the completed near net shape componentfollowing infiltration and during removal of a gate.

FIG. 13 is a perspective view of an attachment PSP for use in aleading-edge repair process.

FIG. 14 is a perspective view of a leading-edge replacement componentattached to the attachment PSP of FIG. 13.

FIG. 15 is a perspective view of a portion of a gas turbine blade havingoperating damage in the form of tip corrosion and tip cracking.

FIG. 16 is a perspective view of the blade of FIG. 15 with the damagedportion of the blade removed.

FIG. 17 is a perspective view of a replacement tip for the repair of thedamaged blade of FIG. 16.

FIG. 18 is a perspective view of an attachment PSP for use in repairingthe blade tip of FIG. 16.

FIG. 19 is a perspective view of the damaged blade of FIG. 16, theattachment PSP of Fog. 18, and the replacement tip of FIG. 17.

FIG. 20 is a perspective view of replacement tip in a “green-form”during the manufacturing process.

FIG. 21 is a perspective view of the replacement tip of FIG. 20 aftersintering and removal from the manufacturing support member.

FIG. 22 is a perspective view of the replacement tip of FIG. 21installed onto the blade of FIG. 16.

FIG. 23 is a perspective view of a gas turbine vane with a damagedportion removed.

FIG. 24 is a perspective view of a pre-sintered preform (PSP)replacement piece and a PSP attachment piece sized to repair the damagedportion of FIG. 23.

FIG. 25 is a perspective view of the pre-sintered preform (PSP)replacement piece of FIG. 24.

FIG. 26 is a flowchart illustrating one process for forming a PSP.

FIG. 27 is a flowchart illustrating an alternative process for forming aPSP.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

Various technologies that pertain to systems and methods will now bedescribed with reference to the drawings, where like reference numeralsrepresent like elements throughout. The drawings discussed below, andthe various embodiments used to describe the principles of the presentdisclosure in this patent document are by way of illustration only andshould not be construed in any way to limit the scope of the disclosure.Those skilled in the art will understand that the principles of thepresent disclosure may be implemented in any suitably arrangedapparatus. It is to be understood that functionality that is describedas being carried out by certain system elements may be performed bymultiple elements. Similarly, for instance, an element may be configuredto perform functionality that is described as being carried out bymultiple elements. The numerous innovative teachings of the presentapplication will be described with reference to exemplary non-limitingembodiments.

Also, it should be understood that the words or phrases used hereinshould be construed broadly, unless expressly limited in some examples.For example, the terms “including,” “having,” and “comprising,” as wellas derivatives thereof, mean inclusion without limitation. The singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. Further, the term“and/or” as used herein refers to and encompasses any and all possiblecombinations of one or more of the associated listed items. The term“or” is inclusive, meaning and/or, unless the context clearly indicatesotherwise. The phrases “associated with” and “associated therewith,” aswell as derivatives thereof, may mean to include, be included within,interconnect with, contain, be contained within, connect to or with,couple to or with, be communicable with, cooperate with, interleave,juxtapose, be proximate to, be bound to or with, have, have a propertyof, or the like. Furthermore, while multiple embodiments orconstructions may be described herein, any features, methods, steps,components, etc. described with regard to one embodiment are equallyapplicable to other embodiments absent a specific statement to thecontrary.

Also, although the terms “first”, “second”, “third” and so forth may beused herein to refer to various elements, information, functions, oracts, these elements, information, functions, or acts should not belimited by these terms. Rather these numeral adjectives are used todistinguish different elements, information, functions or acts from eachother. For example, a first element, information, function, or act couldbe termed a second element, information, function, or act, and,similarly, a second element, information, function, or act could betermed a first element, information, function, or act, without departingfrom the scope of the present disclosure.

In addition, the term “adjacent to” may mean: that an element isrelatively near to but not in contact with a further element; or thatthe element is in contact with the further portion, unless the contextclearly indicates otherwise. Further, the phrase “based on” is intendedto mean “based, at least in part, on” unless explicitly statedotherwise. Terms “about” or “substantially” or like terms are intendedto cover variations in a value that are within normal industrymanufacturing tolerances for that dimension. If no industry standard asavailable a variation of 20 percent would fall within the meaning ofthese terms unless otherwise stated.

FIG. 1 illustrates a gas turbine or combustion turbine engine 10 thatincludes a compressor section 15, a combustion section 20, and a turbinesection 25. During operation, atmospheric air is drawn into thecompressor section 15 and compressed. A portion of the compressed air ismixed with a fuel and combusted in the combustion section 20 to producehigh-temperature products of combustion. The products of combustion aremixed with the remaining compressed air to form exhaust gas that thenpasses through the turbine section 25. The exhaust gas expands withinthe turbine section 25 to produce torque that powers the compressorsection 20 and any auxiliary equipment attached to the engine 10, suchas an electrical generator. The exhaust gas enters the turbine section25 at a high temperature (1000 degrees F., 538 degrees C. or greater),such that the turbine blades 30 and vanes are exposed to hightemperatures and must be manufactured from materials suited to thosetemperatures. The terms “blade” and “vane” should be read as beinginterchangeable. While typically, the term “blade” refers to rotatingair foils and “vane” refers to stationary airfoils, the invention shouldnot be limited to these definitions as most repairs or processes areequally applicable to both blades and vanes.

In one construction, the vanes 30 are manufactured from a nickel-basedsuperalloy such as Alloy (CM) 247. FIG. 2 illustrates a portion of thestationary vanes 30 from the turbine section 25 of the engine 10 ofFIG. 1. Each vane 30 includes a leading edge 35, a trailing edge 40, asuction side 45, and a pressure side 50. Adjacent vanes 30 cooperatewith one another to define a flow path therebetween. The exhaust gaspasses through the flow paths and is directed and accelerated as desiredto provide an efficient expansion of the exhaust gas and to providetorque to a rotor 53 that in turn drives the auxiliary equipment.

During operation, the vanes 30 can become damaged. Damage can be causedby foreign object impacts, high temperature operation, fatigue, creep,oxidation, and the like. One area that is susceptible to damage is theleading edge 35 of the vane 30. FIG. 2 illustrates one of the vanes 30with a portion 55 of the leading edge 35 removed. A desired repair wouldinclude replacing the removed portion 55 with a material that closelymatches the base material. However, nickel-based superalloys such asthose used to manufacture the vanes 30 are not conducive to welding ortypical additive manufacturing repair processes.

FIGS. 3 and 4 illustrate one possible repair for the leading edge 35 ofthe vane 30 illustrated in FIG. 2. FIG. 3 illustrates an insert piece inthe form of a leading edge insert 60 and FIG. 4 illustrates thepositioning of the leading edge insert 60 in the vane 30 for attachment.The insert 60 includes a substantial portion of matching base materialand is typically attached using a brazing process.

FIGS. 5-12 illustrate a process for manufacturing the insert piece 60illustrated in FIG. 3 or any other repair component desired. FIGS. 5-8illustrate the process for a generic cube-shaped object 65 while FIGS.9-12 illustrate a similar process for the leading edge insert 60illustrated in FIG. 3.

The process begins by mixing a high gamma prime nickel powder 66 (basematerial) with a binder 67 and 3D printing or otherwise additivelymanufacturing a green form of the desired component 70, 75 to a near netshape. The green form component 70, 75 is then allowed to dry. FIGS. 5and 9 illustrate this step. During the printing or additivemanufacturing process, the base material is not melted. As used herein,the term “near net shape” means that the component falls within thedesired manufacturing parameters and tolerances for the component at aparticular step in the manufacturing process without further machining.However, some surface grinding or polishing may be required to achieve adesired surface finish or texture for the final component. In addition,additional layers or coatings may be applied to the component tocomplete the component for use. Furthermore, and as illustrated in FIGS.9-12 the green form component 75 may include features such as gates 80,or support structures that are used during the manufacturing process andthen removed. The green form component 75, including features such asthese would be considered near net shape as additional machining orprocessing is not required before the additional manufacturing steps areperformed and all that is required is the removal of the unwantedfeatures (gate 80).

The next step is the placement of the green form component 70, 75 into afurnace or other heating device. The green form component 70, 75 isheated to burn or remove the binder 67. The remaining material defines askeleton 85, 90 made up of the base material 66 and gaps or empty areas68 formerly occupied by the binder material 67. In FIG. 6, the skeleton85 is a cube-shape. In FIG. 10 the skeleton 90 defines an intermediatecomponent that will ultimately become the leading edge insert 60 andfurther includes the gate 80. In preferred arrangements, the heating orsintering step does not melt the base material 66 and leaves at leasteighty percent of the volume of the skeleton 85, 90 as base material 66,thereby leaving no more than twenty percent of the skeleton 85, 90 asempty space 68. This is referred to herein as twenty percent porosity orless. The amount of binder 67 used, and the sintering temperature areselected to arrive at less than twenty percent porosity and preferablybetween five percent and twenty percent porosity.

As illustrated in FIGS. 7 and 11, the skeleton 85, 90 and the gate 80are infiltrated with low melting point material, or melting pointdepressant 100 (sometimes referred to as braze material). Preferredcompositions of the melting point depressant 100 include at least one oftitanium (Ti), zirconium (Zr), and hafnium (Hf) with the balance beingchromium (Cr) and nickel (Ni). The use of boron (B), silicon (Si), orphosphorous (P) in part or in whole as the melting point depressant 100is avoided to prevent the negative effects these materials have on thematerial properties of the completed component 60, 65.

To produce the desired infiltration, the melting point depressant 100 ismelted in a manner that assures that the liquid melting point depressant100 is in contact with the skeleton 85, 90. Capillary action produced bythe porosity in the skeleton 85, 90 pulls the liquid melting pointdepressant 100 into the pores 68 of the skeleton 85, 90 and can resultin a completed component 60, 65 that is ninety-nine percent filled withmaterial (i.e., one percent porosity).

The specific composition of the melting point depressant 100 is selectedbased at least in part on the quantity of titanium included in the basematerial. For example, in constructions that include 3.5 percent or moretitanium by weight in the base material, the desired melting pointdepressant 100 includes at least one of Hf and Zr with the remainderbeing Ni and Cr. In constructions with 1.0 percent or less Ti in thebase material, the preferred composition includes Ti with the balancebeing Ni and Cr. When the quantity of Ti is between 1.0 percent and 3.5percent in the base material, the desired composition includes at leastone of Zr, and Ti with the balance being Ni and Cr. The quantity of Ti,Zr, or Hf are selected such that the completed nickel-based componenthas less than 6.0 percent Ti (with other constructions being below 5.0percent and still others below 4.0 percent).

Once the infiltration is complete, any features added for manufacturingrequirements such as the gate 80 or a support structure illustrated inFIGS. 9-12 are removed to complete the component 60, 65. Any additionalgrinding, polishing, or layer additions can now be performed prior tothe installation of the component 60, 65 as illustrated in FIG. 4. Inpreferred constructions, following infiltration, the component 60, 65has less than one percent porosity.

The process described herein does not melt the base material powder 66.Rather, the powder 66 is mixed with the binder 67, 3D printed using alaser source or other energy source and dried. The binder 67 is burnedout at low temperature (e.g., <500C). The remaining base material 66 isheated up to a sintering temperature that assures a maximum of twentypercent porosity is left in the sintered material.

For nickel-based alloys, the amount of titanium employed is preferablylimited to around six percent (i.e., between four and eight percent) toreduce the likelihood of reduced mechanical properties. Due to thislimitation, the level of porosity in the skeleton 85, 90 is determined,at least in part by the amount of titanium in the base material and inthe braze material 100 (sometimes referred to as melting pointdepressant) with the goal being about six percent titanium in thefinished component 60, 65. For example, in one construction, the basematerial or the skeleton 85, 90 may include no titanium. If a brazematerial that contains 22% titanium is employed, the total porosity ofthe skeleton 85, 90 would be limited to about 30% which leads to acompleted component 60, 65 with about 6.6% titanium.

In another example, the skeleton 85, 90 includes 1% titanium. In thiscase, using the same braze material with 22% titanium, the skeleton 85,90 should be limited to less than 20% porosity to arrive at a finishedcomponent 60, 65 having about 5.2% titanium.

In yet another example, the skeleton 85, 90 includes 2% titanium. Inthis case, using the same braze material with 22% titanium the skeleton85, 90 should be limited to less than 15% porosity to arrive at afinished component 60, 65 having about 6.0% titanium.

As discussed, nickel-based gas turbine components, specifically Alloy(CM) 247 components, are difficult to repair or build-up with any methodthat involves melting of the component since the grain boundary melting(incipient melting) temperature is low with respect to the weldingtemperature such that the weld repair often generates cracks during therepair process.

As discussed with regard to FIGS. 2-12, one alternative to weld repairis to first build a replacement component 60, 65 (a pre-sintered preform(PSP)) for the damaged section of the vane 30 and then join this newreplacement component 60, 65 to the component being repaired (e.g., vane30) using a process that assures a maximum temperature that remainsbelow the grain boundary melting temperature. To further improve thisrepair, one could replace the damaged section of the component beingrepaired with a replacement component 60, 65 that includes a functionalmaterial that provides a higher oxidation resistance than the basematerial of the component being repaired (e.g., vane 30).

The damaged portion 55 is removed and replaced with a close-fittingreplacement component 105 made using additively manufactured (AM)material or a pre-sintered preform (PSP) that provides similar or betteroxidation and rupture properties. When the replacement component 105 isa replacement for the leading edge 35 as illustrated in FIGS. 2-4 and9-12, additively manufactured replacement components 105 can includecolumnar grains with significant rupture capability.

To perform a repair of the leading edge 35 with a high oxidationresistant material, the damaged portion 55 of the leading edge 35 of thevane 30 is first removed. The removed damaged portion 55 is measured todetermine the size and configuration of the replacement component 105that will be installed. The replacement component 105 is thenmanufactured using an additive manufacturing process or as a PSP, suchas a PSP made using a process as described with regard to FIGS. 2-12. Toenhance the oxidation resistance of the replacement component 105, thematerial used to manufacture it, when using an additive manufacturingprocess includes up to eight percent (8%) aluminum. In addition,attachment structures 110 such as pins, protrusions, notches, apertures,etc. can be formed as part of the replacement component 105 to enhanceor create an interlock between the replacement component 105 and thevane 30 or other component being repaired.

When the replacement component 105 is manufactured as a PSP thepreferred material includes up to eighty percent (80%) superalloy(preferably matching the vane 30 being repaired), up to eight percent(8%) aluminum, and up to thirty percent (30%) braze material includingTi, Zr, and Hf as described above. As with the additively manufacturedreplacement component 105, the PSP replacement components 105 caninclude attachment structures 110 like those described above. FIGS. 9and 10 illustrate attachment structures 110 in the form of alignmentpins 111. The pins 111 align with and engage apertures formed in theblade 30 to which the replacement component 105 will attach. While thepins 111 are illustrated in only FIGS. 9 and 10 for clarity, inpreferred constructions the pins 111 would be formed as part of thereplacement component 105 and would therefore be present at each step ofthe manufacturing process. In other constructions, the pins 111 areseparate components that are attached to the replacement component 105at some point during its manufacture. Attachment could be facilitatedusing any suitable attachment means including but not limited toadhesives, welding, brazing, etc.

The material used to manufacture the PSP replacement component 105 ismaintained at a temperature at least 50 degrees C. above the brazemelting temperature for more than one hour to react a majority of thebraze material with the base material powder. This prevents re-meltingduring the braze operation that attaches the replacement component 105to the vane 30.

An attachment PSP 115, shown in FIG. 13 is formed from a materialcombination similar to that described above with regard to the PSPreplacement component 105 with the exception that it includes at leastthirty percent (30%) braze material rather than up to thirty percent(30%) braze material. The attachment PSP 115 is preferably no more than250 microns thick and is produced at a similar temperature as the PSPreplacement component 105 described above but is held at thattemperature for a shorter time (less than 15 minutes). The attachmentPSP 115, therefore has enough unreacted braze material to be able tojoin the replacement component 105 as illustrated in FIG. 14, regardlessof how it is manufactured (PSP or additive manufacturing) to the vane 30being repaired.

The replacement component 105 has sufficient mechanical properties andoxidation resistance due to the adjusted composition and the Ni—Cr—(Ti,Zr, Hf) braze composition. In addition, when using the additivelymanufactured replacement component 105, the columnar grains providesignificant rupture capability over the base material of equiaxed grainstructure.

It should be noted that the replacement component 105 can bemanufactured in a number of different shapes and sizes and shouldtherefore not be limited to the arrangement illustrated in FIGS. 2-4 and9-14. For example, FIGS. 23-25 illustrate a leading-edge repair thatutilizes a replacement piece 250 (shown in FIGS. 24 and 25 and sometimesreferred to as a replacement piece) that includes a curved interfacesurface 255 as compared to the more rectangular or linear interfacesurface of FIGS. 2-4.

Specifically, and with reference to FIG. 23, a leading-edge 260 of astationary vane 265 is illustrated with a portion removed. The removedportion 270 likely included damage such as cracks, spallation, impactdamage, and the like that rendered it unsuitable for use. The damagedmaterial, along with undamaged material is removed to define a vaneinterface 275 that is curved. The vane interface 275 could follow anelliptical or circular arc (when viewed in the circumferentialdirection) or any other curve desired. It is preferred that a continuouscurve (when viewed in the circumferential direction), in themathematical sense be employed but non-continuous curves or surfacescould be employed as well. The stationary vane 265 of FIG. 23 includes apressure side surface and a suction side surface spaced from thepressure side surface to define a hollow space. In this arrangement, afirst interface surface is formed on the pressure side surface and asecond interface surface is formed on the suction side surface. Inpreferred constructions, each of the first interface surface and thesecond interface surface follows the same continuous curve (when viewedin the circumferential direction). However, some constructions mayemploy different curves. In addition, as will be understood, theinterface surfaces follow a complex three-dimensional path. However,when that path is projected onto a plane in the circumferentialdirection, that curve is preferably a continuous curve.

With the damaged portion removed, the replacement piece 250 can bemanufactured. The replacement piece 250 could be manufactured using anyof the various processes described herein and is manufactured to includethe replacement surface 255 that is curved to closely match the vanesurface 275 formed in the vane 265 through the removal of the damagedportion 270. In addition, any cooling holes 285 or other internalfeatures (e.g., ribs, etc.) are typically preformed in the replacementpiece 250 before it is attached to the vane 265.

The replacement surface 255 illustrated in FIG. 25 includes a thirdinterface surface and a fourth interface surface that are each curved tomatch the curves of the first interface surface and the second interfacesurface. Specifically, in preferred constructions, the third interfacesurface and the fourth interface surface define a continuous curve whenprojected in the circumferential direction onto a two-dimensional plane.Of course, the actual shape of the curve or curves is selected to matchthe first interface surface and the second interface surface.

As illustrated in FIG. 24, a PSP interface component 290 may also bemanufactured to closely match the shape of the replacement surface 255and the vane interface surface 275. PSP interface components 290 areused to enhance the attachment of the replacement piece 250 to the vane265 when material considerations or other considerations make itnecessary. Of course, in some constructions, the PSP interface component290 is not needed.

The replacement piece 250, and the PSP interface component 290, ifneeded are positioned as illustrated in FIG. 24 such that they closelyfit one another. A braze process is then performed using any of thebraze materials discussed herein or any other braze material suitablefor use with the particular materials of the vane 265 and thereplacement piece 250 and the process in which the vane 265 ultimatelyoperates. Once the braze is complete, the repaired vane 265, or othercomponent can be finished with any processes that might be necessary forthe particular component (e.g., machining, grinding, polishing, coatingapplication, etc.).

As will be described below, these processes and procedures can beapplied to other components such as a tip 120 of the vane 30 or blade orsome other component.

For example, FIGS. 15-19 illustrate a process similar to that justdescribed but for the repair of the tip 120 of a nickel-based gasturbine vane 30 or blade, and specifically a vane 30 or blade made fromAlloy 247 or a similar material.

FIG. 15 schematically illustrates the blade 30 with tip section cracks125 that extend downward in the blade 30. The blade tip 120 alsoincludes oxidation damaged portions 130 that can be common followingoperation of the turbine blade 30. In order to repair the blade 30, thedamaged portion of the tip 120 is first removed. In the example of FIG.15, the removal of the damaged portion 135 does not completely removethe cracks 125 but does remove the oxidation damaged portions 130. It isdesirable to minimize the amount of the tip 120 being removed such thatin some circumstances, portions of the crack or cracks 125 may remainafter removal. With reference to FIG. 16, any cracks 125 that remainafter the removal of the damaged portion 135 are removed using amachining process, grinding, or other suitable material removalprocesses.

A closely fitting replacement tip 140 is formed to fill the spacecreated by the removal of the damaged portion 135. The replacement tip140 may also fill any spaces created during the removal of any cracks125. Alternatively, the space opened during the removal of the cracks125 can be filled with a powdered braze material during the attachmentprocess for the replacement tip 140. The replacement tip 140 can beformed using an additive manufacturing (AM) process or can be formedfrom a pre-sintered preform (PSP) that provides similar or betteroxidation and rupture properties than the removed portion 135.

The replacement tip 140, when manufactured using an AM process ispreferably composed of a material similar to the base material of theblade 30 with the addition of up to eight percent (8%) aluminum toprovide superior oxidation resistance. In addition, attachmentstructures 110 such as pins 145, illustrated in FIG. 17, can be used toenhance the mechanical connection between the replacement tip 140 andthe remainder of the blade 30 being repaired. Of course, other featuressuch as protrusions, apertures, bosses, etc. can be used as attachmentstructures 110. The pins 145 of FIG. 17 are received in correspondingapertures formed or otherwise existing in the remaining portion of theblade 30 being repaired.

In constructions in which a PSP is used in place of an AM replacementtip 140, the material is preferably made of up to eighty percent (80%)superalloy (matching the base material of the blade 30 being repaired),up to eight percent (8%) aluminum, and up to thirty percent (30%) brazematerial including Ti, Zr, and Hf as described above.

The material used to manufacture the PSP replacement tip 140 ismaintained at a temperature at least 50 degrees C. above the meltingtemperature of the braze material for more than one hour to react amajority of the braze material with the base material powder. Thisprevents re-melting during the braze operation that attaches thereplacement tip 140 to the blade 30 being repaired.

A tip attachment PSP 150, shown in FIG. 18 is formed from a materialcombination similar to that described above with regard to the PSPreplacement tip 140 with the exception that it includes at least thirtypercent (30%) braze material rather than up to thirty percent (30%)braze material. The tip attachment PSP 150 is preferably no more than250 microns thick and is produced at a similar temperature as the PSPreplacement tip 140 described above but is held at temperature for ashorter period of time (less than 15 minutes). The tip attachment PSP150 therefore has enough unreacted braze material to be able to join thereplacement tip 140 to the blade 30 being repaired as illustrated inFIG. 19, regardless of how the replacement tip 140 is manufactured (PSPor additive manufacturing).

The replacement tip 140 has sufficient mechanical properties andoxidation resistance due to the adjusted composition and the Ni—Cr—(Ti,Zr, Hf) braze composition.

As discussed earlier, gas turbine components operate under a variety oflocalized conditions that can produce localized damage. This can beattributed to varied component conditions (e.g., temperatures,pressures, fluid properties, etc.) and engine conditions.

One example of localized operating conditions exists at the row oneturbine blade 155 where localized distress on the blades 155 can causedamage in multiple areas including a leading edge 160 of the blade 155and a tip 165 of the blade 155. FIG. 22 illustrates the leading edge 160and the tip 165 of the blade 155 and also illustrates a replacement tip170 installed to repair cracking and/or oxidation damage at the bladetip 165.

One type of damage occurs at the leading edge 160 of the first stageblade 155, as well as other blades where the ceramic coating adheresadjacent a series of cooling apertures 175. If the coating spalls, aleading edge burn out or loss is often observed. The other area wheredamage can occur is at the tip 165 of the blade 155 where the blade 155can rub against a ring segment or other component radially outward ofthe blade 155. Heavy oxidation can also occur at the tip 165 of theblade 155 and cracks or tip cracks can form and propagate from coolingapertures 175 or from damage caused by other factors such as rubbing oroxidation.

As discussed previously, repairs to blade or vane tips 165 can includethe removal of a portion of the blade tip 165 followed by replacementwith a replacement tip 170. Similar repairs can also be made to blade orvane leading edges 160.

Additive manufacturing can be relied upon to manufacture replacementcomponents or replacement tips 170 with brazing processes and specialbraze materials enhancing the operation of the repaired vane or blade155.

One preferred additive manufacturing process well-suited tomanufacturing replacement components or replacement tips 170 includesatomic diffusion. FIGS. 20-22 illustrate the process of repairing theblade tip 165 using atomic diffusion to form the replacement tip 170. Asone of ordinary skill will realize, the same process could be applied tothe repair of the leading edge 160 of the blade 155 or vane as well asto other components not discussed herein.

With reference to FIG. 20, atomic diffusion uses binding agents and ametal powder for rapid construction of a 3D shape. The metal powder isgenerally selected to closely match the material (e.g., Alloy (CM) 247)used in the component (i.e., the blade 155) being repaired. The metalpowder and the polymeric binding agent are mixed and then formed intothe desired shape that will ultimately result in the replacementcomponent or tip 170. This preliminary component 185 is often referredto as a “green-form”. The “green-form” component 185 is then heated andsintered in a high temperature sintering operation to remove the bindingagent and mechanically/metallurgically bond the powder particles. Thesintering temperature is selected to fully remove the binding agentwhile providing the desired mechanical/metallurgical bond of thepowdered metal without fully melting the powdered metal particles.

One method of forming the green-form component 185 includes a 3-Dprinting technique. A wire feedstock is prepared including the desiredpowder metal and the binder. The user is able to combine materialchemistries or tailor chemistries as desired to achieve the desiredmaterial properties in the completed replacement tip 170 or replacementpiece. In addition, different compositions can be used at differenttimes during the forming of the replacement tip 170 to achieve differentproperties at the different locations within the replacement tip 170.For example, in one construction a composition intended to be a first orinterfacing layer includes the desired base materials as well as brazematerial integrated into the wire feedstock.

To manufacture the replacement tip 170 or another component, the firstor interfacing layer is deposited onto a support structure 190 or isformed independent of the support structure 190. The first surface inthe example of FIG. 20 is intended to be the surface that interfaces oris brazed to the component being repaired (i.e., the blade 155) toattach the replacement tip 170 to the blade 155 being repaired.Additional layers may be formed on top of the first layer using the samematerial, or another material may be used as may be required for theparticular replacement component.

For example, the feedstock could be changed to a second material thatdoes not include the braze material and rather, more closely matches thebase material of the blade 155 or other component being repaired. Asdiscussed above, some materials could be employed that enhance theperformance of the replacement tip 170 or other component over that ofthe base material. Any of those materials could be employed in thisprocess as well. For example, up to 8% aluminum could be employed toenhance oxidation resistance. As previously noted, the sintering processis designed to not melt the powdered material. Because the process is anon-melting process, no variation in chemistry is expected.

With continued reference to FIG. 20, the metal powder is extruded withthe binder (e.g., a polymer) to create the wire feedstock that is thendeposited onto the support structure 190. A ceramic interlayer 195 maybe positioned between the deposited material and the support structure190 to aid in the removal of the completed replacement tip 170 from thesupport structure 190. A washing step of the green structure removes thepolymer binder and densification is performed via sintering. Typically,densities of greater than ninety-six percent can be achieved but this isdependent on component size and corresponding wall thickness, since thedensification is achieved by solid stage diffusion. Examples ofreplacement tips 170 formed using this process, after sintering andremoved from the support structure are illustrated in FIG. 21.

This method does not experience the isotropy of layer-based AMtechniques and because of its speed in producing the green-formcomponent 185 and very low powder waste, reduces cost significantly overother AM techniques. In addition, as noted earlier this process ofadditive manufacturing can be used to form components other thanreplacement tips 170, including leading edge replacements or othercomponents and can include advanced features such as attachmentstructures 110.

Another benefit with this approach is that the components can be madefrom other high temperature resistant materials (e.g., oxide dispersionstrengthened (ODS) or advanced single crystal (CMSX8/Rene N5/PWA1484))that have better strength, oxidation resistance, and coating adhesion.

In summary, FIGS. 20-22 illustrate a replacement tip 170 during variousstates of manufacture using the atomic diffusion process. After removalof the damaged portion of the tip 165 of the blade 155 being repaired,the replacement tip 170 can be sized for manufacture. In many cases, thesupport structure 190 will be needed to define a base of support ontowhich the replacement tip 170 can be formed. While not required, insituations where the support structure 190 is used, a ceramic interlayer195 may be first applied to aid in easily separating the completedreplacement tip 170 from the support structure 190.

The green-form component 185 is next printed using feedstock of theappropriate makeup. The first layer, or the first few layers may use afeedstock that is part base material, part binder, and part brazematerial that ultimately is used during the attachment of thereplacement tip 170 to the blade 155. After these initial layers areprinted, the feedstock may be switched to a feedstock that includes thedesired base metal chemistry (i.e., a chemistry closely matching theblade 155) and a binder, often in the form of a polymer. The chemistryof the subsequent feedstock may include an enhanced chemical make-up asdiscussed earlier to provide superior material properties such asoxidation resistance.

Upon completion of the 3-D printing process, the green-form component185 is washed and sintered to remove the binder and to mechanically ormetallurgically bond the remaining particles in the desired shape. Thesintered replacement tip 170 is removed from the support structure 190as illustrated in FIG. 21.

As illustrated in FIG. 22, the replacement tip 170 is placed in positionon the blade 155 and a braze joint 200 is formed therebetween. Duringthe brazing process, braze material in the initial layer or layers ofthe replacement tip 170 facilitates the completion of the braze jointand the attachment of the replacement tip 170.

Current materials used for pre-sintered preforms (PSPs) and for brazingmaterials for use with nickel-based super alloy materials that operatein high temperature environments (e.g., 1000 degrees F., 538 degrees C.)are typically nickel (Ni) chromium (Cr) based.

The composition described herein is preferably applied to PSPs and/orbraze materials that do not include boron. To improve the creep rupturelife of boron-free PSPs and braze materials, rhenium (Re) or Ruthium(Ru) can be added to most nickel-based braze alloys. These two elementsare potent creep resistance elevators that are added to base metalcomposition for creep-rupture life improvement. They increase the creepresistance of nickel-base alloys by up to a factor of ten. Their highmelting point and large atomic diameter results in low atomic diffusionrates and enables Ni base materials to increase their creep resistance.

Rhenium (Re) and Ruthium (Ru) have not been added to boron-free brazematerials to date as the need for creep resistance braze materials wasnot known.

To add Re or Ru, the materials are powdered and then mixed with a basematerial powder mixture prior to brazing. Re and Ru are added to boronfree Ni—Cr—X braze/base material powder mixture prior to PSP making.Preferably, the Re and Ru have the smallest particle size possible forthe powder. It is preferred that Re and Ru powder diameter is at least50% or smaller than the base metal and braze metal powder to assureuniform mixing and homogeneous elemental distribution after brazing. Reand Ru powders are not melted during the brazing process. Rather theydiffuse into the surrounding liquid braze material during braze. Sincediffusion rates are high in liquid, these elements are transporteduniformly within the braze material.

Re and Ru are added such that they make up 3-6 percent of the totalcomposition of the braze or PSP regardless of the proportion of basemetal to braze powder in the braze.

For example, the repair of a component manufactured from Alloy 247 mayemploy a PSP that is manufactured from powders in which 74-77 percentmatches the Alloy 247 composition, 20 percent matches a desired brazematerial (sometimes referred to as a melting point depressant), and 3-6percent is one or both of Re or Ru.

Suitable braze materials are typically nickel-based and include nickel,chromium, and at least one of titanium, zirconium, and hafnium. Somespecific braze compositions include a composition that includes 6.5% Cr,11% Zr, 7.5% Ti, and the remainder Ni. Another composition could include5.0% Cr, 10% Hf, 10% Zr, and the remainder Ni. Yet another compositioncould include 17% Cr, 22% Ti, and the remainder Ni.

Each of the three components, the base material (74-77 percent), thebraze material (20 percent), and the Re or Ru (3-6 percent) are powderedand mixed together for sintering. During any melting steps (i.e. brazingprocesses), the Re and Ru are not melted. Rather, they disperse throughany melt pools during the melting process.

FIG. 3 illustrates one possible PSP insert 60 that could be manufacturedusing the above-described materials. The PSP insert 60 is preformed andsintered to include base material, a braze material, and the desiredquantity of Re or Ru. FIG. 4 illustrates the repair of a turbine vane 30using the PSP insert 60 illustrated in FIG. 3. After the damaged portionof the vane 30 is removed, the required PSP insert 60 is sized andmanufactured as described. The PSP insert 60 is then positioned in theempty space 55 in the vane 30 and brazed into place. During the brazingprocess, some of the Re and Ru will migrate into the liquid braze. TheRe and Ru will not melt in the pool but rather will become embedded inthe braze material during solidification.

Nickel-based superalloys that include more than about two percentaluminum are known to be particularly difficult to weld or to form usingpresent additive manufacturing techniques. Components, parts ofcomponents, or preforms using these materials can be manufactured usinga process similar to that described above. In one example, a preform(e.g. preforms 105, 250, etc.) with a nickel-based superalloy that mayinclude at least 4.5 percent aluminum is formed. Of course, the systemand process can be used with virtually any desired material. In oneprocess, illustrated in FIG. 26 a pre-sintered preformed (PSP), such asthe one illustrated in FIGS. 23-25 is formed for the repair or themanufacture of a component having a base material that is a nickel-basedsuperalloy with more than 4.5% percent aluminum. To form the PSP amixture of powdered base material, a braze material, and a binder ismade (step 500). For gas turbine applications, a mixture of 80 percentbase material and 20 percent braze material is suitable, with binderadded as required to meet the requirements of the additive manufacturingprocess being employed (step 505). The mixture is made to be suitablefor use in a micro-dispensing additive manufacturing system such asthose used and sold by ηSCRYPT of Orlando Fla. (step 510).Micro-dispensing AM systems can dispense the mixture in layers that areas thin as 10 microns and as thick as 100 microns with preferredthicknesses being 20 microns to 50 microns.

The micro-dispensing AM system is then operated to dispense the mixturein a series of layers that define the desired shape of the PSP (step515) (e.g., replacement piece 250, PSP interface component 290, etc.).Preferably, each layer is between 20 microns and 100 microns inthickness with other thicknesses being possible. The use of themicro-dispensing AM system allows for very fine control including theuse of a CNC model to drive the positioning of the layers to improve theaccuracy and finish of the final component.

Once the micro-dispensing AM process is completed, the component isremoved from the device and is heated to a temperature less than 500degrees C. but hot enough to remove the binder from the component (step520). At the completion of this process, a component skeleton is formedthat includes base material and braze material in the ratio selected forthe mixture and gaps where the binder material was prior to its removalin the first heating process.

The component skeleton is then heated to a solid-state sinteringtemperature that for this material falls within the range of 1000degrees C. to 1250 degrees C. (step 525). Typically, the solid-statesintering process requires less than 60 minutes to complete. Of course,other materials or mixtures having different ratios of the base materialand braze material may have different solid-state sintering temperaturesand may require more time to complete the solid-state sintering.

A second sintering process is then performed on the now sinteredcomponent skeleton (step 530). Specifically, the component is heated toa braze temperature range of between 1250 degrees C. and 1300 degrees C.for less than 60 minutes to melt all or some of the braze material, butnot the base material, thereby completing a liquid-phase sinteringprocess. Of course, other materials or mixtures having different ratiosof the base material and braze material may have different liquid-phasesintering temperatures and may require more time to complete thesolid-state sintering.

To complete the formation of the skeleton component, the skeletoncomponent is again heated to a solution treatment temperature range ofbetween 1230 degrees C. and 1300 degrees C. for between 1 and 12 hoursto complete a diffusion annealing process (step 535). Of course, othermaterials or mixtures having different ratios of the base material andbraze material may have different diffusion annealing temperatures andmay require more time to complete the diffusion annealing process.

Following these steps allows for the sintering of the component withoutmelting and solidifying the base material (high gamma prime powder) suchthat the component is not prone to cracking.

One variation of the process just described, illustrated in FIG. 27utilizes a mixture of base material and binder with no braze material(step 540). The component is 3d printed using the micro-dispensing AMprocess described above. A second mixture containing a braze and bindermixture is then applied to some or all the outer surfaces of thecompleted component using the micro-dispensing AM process or anotherprocess if desired (step 545). The various heating processes describedabove are then performed. During the liquid-phase sintering process, thebraze melts and infiltrates the base metal powder of the component.

In another variation, of the just-described process, the component iscovered or partially covered with either a 100 percent braze materialbinder mixture or a base material powder, a braze material powder, and abinder mixture. The sintered skeleton is ultimately infiltrated by thebraze to obtain a near 100 percent dense component.

In all the processes just described, the braze material is preferablyone of a Ni—Cr—Ti or a Ni—Cr—Ti—Zr braze. In addition, theaforementioned processes generally allow for the avoidance of a HIP (HotIsostatic Pressing) operation as the liquid phase infiltration resultsin a near 100 percent dense structure (typically at least 99.9 percent).

As discussed, the above processes can be used to form components usinghigh gamma prime powder which does not melt in this process such thatresidual stresses that cause cracking and may be created duringsolidification are not present.

The micro-dispensing AM process can produce layers having thicknesses aslow as 10 microns. In addition, PSP components or panels can be builtand used to join nickel and cobalt base alloys including Ni—Cr—Ti andNi—Cr—Ti—Zr. In addition, these materials and the micro-dispensing AMprocess can be used to produce foils having a total thickness of 50microns or less (e.g. PSP interface component 290). In addition, themicro-dispensing AM process allows for the production of near net shapecomponents using high gamma prime materials without cracking. While an80/20 (base material/braze material) powder mix is preferred for gasturbine applications, some applications may include up to 30 percentbraze material.

It should be noted that while the foregoing examples describe theformation of PSP components separate from the components being repaired,some repairs may include printing the PSP preform directly onto thecomponent being repaired. Thus, the invention should not be limited toPSPs that are formed separate from the component they are being made torepair.

Although an exemplary embodiment of the present disclosure has beendescribed in detail, those skilled in the art will understand thatvarious changes, substitutions, variations, and improvements disclosedherein may be made without departing from the spirit and scope of thedisclosure in its broadest form.

None of the description in the present application should be read asimplying that any particular element, step, act, or function is anessential element, which must be included in the claim scope: the scopeof patented subject matter is defined only by the allowed claims.Moreover, none of these claims are intended to invoke a means plusfunction claim construction unless the exact words “means for” arefollowed by a participle.

What is claimed is:
 1. A method of repairing a component comprising:removing a damaged portion from the component to leave a first interfacesurface that is defined by a continuous curve; mixing a powdered basematerial and a binder to define a mixture; printing the mixture into adesired shape without melting the base material; removing the binderfrom the desired shape; solid-state sintering the desired shape to forma replacement piece having a second interface surface that is defined bythe continuous curve; liquid-phase sintering the replacement piece tomelt a braze material applied to the replacement piece, the brazematerial filling space created by the removal of the binder; andattaching the second interface surface to the first interface surface toreplace the damaged portion of the component.
 2. The method of claim 1,wherein the desired shape is heated to remove the binder without meltingthe base material.
 3. The method of claim 1, wherein the componentincludes a first side wall and a second side wall spaced apart from thefirst side wall, and wherein the removing the damaged portion stepincludes forming the first interface surface on the first side wall andforming a third interface surface on the second side wall.
 4. The methodof claim 3, wherein the desired shape includes the second interfacesurface arranged to match the first interface surface and a fourthinterface surface arranged to match the third interface surface.
 5. Themethod of claim 4, wherein the first interface surface and the thirdinterface surface are each defined by the same continuous curve.
 6. Themethod of claim 1, wherein the replacement piece is a portion of aleading edge of a turbine vane.
 7. The method of claim 1, wherein theprinting step includes micro-injecting a first layer having a thicknessof between 10 microns and 100 microns.
 8. The method of claim 1, furthercomprising repeating the micro-injecting step to form additional layersto complete the replacement piece.
 9. A method of repairing a componentcomprising: removing a damaged portion from the component to leave afirst interface surface; mixing a powdered base material and a binder todefine a mixture; micro-injecting a layer of the mixture having athickness between 10 microns and 100 microns; repeating themicro-injecting process to form additional layers and complete areplacement piece; heating the replacement piece to remove the binder;sintering the replacement piece; performing a liquid-phase sinteringprocess while adding a braze material, the braze material filling emptyspaces created by the removal of the binder within the replacementpiece; and fixedly attaching the replacement piece to the component toreplace the damaged portion.
 10. The method of claim 9, wherein thesintering step includes a solid-state sintering process.
 11. The methodof claim 9, wherein a temperature of the heating step is selected toremove the binder without melting the base material.
 12. The method ofclaim 9, wherein the component includes a first side wall and a secondside wall spaced apart from the first side wall, and wherein theremoving the damaged portion step includes forming the first interfacesurface on the first side wall and forming a third interface surface onthe second side wall.
 13. The method of claim 12, wherein the desiredshape includes the second interface surface arranged to match the firstinterface surface and a fourth interface surface arranged to match thethird interface surface.
 14. The method of claim 13, wherein the firstinterface surface and the third interface surface are each defined by acontinuous curve.
 15. The method of claim 9, wherein the replacementpiece is a portion of a leading edge of a turbine vane.
 16. Areplacement assembly for replacing a damaged portion of a component, thereplacement assembly comprising: a replacement piece including a firstplurality of layers with each layer of the first plurality of layersformed on top of a prior formed layer of the first plurality of layers,the first plurality of layers arranged to define a curved leading edgeportion and a first interface surface, the interface surface defined bya first continuous curve; and an attachment piece including a secondplurality of layers with each layer of the second plurality of layersformed on top of a prior formed layer of the second plurality of layers,the attachment piece arranged to fit between the first interface surfaceand the component to fixedly attach the replacement piece to thecomponent to replace the damaged portion.
 17. The replacement assemblyof claim 16, wherein layer of the first plurality of layers defines athickness of between 10 microns and 100 microns.
 18. The replacementassembly of claim 16, wherein the replacement piece includes a firstwall that defines the first interface surface and a second wall spacedapart from the first wall that defines a second interface surfacedefined by a second continuous curve.
 19. The replacement assembly ofclaim 18, wherein the first continuous curve and the second continuouscurve are the same.
 20. The replacement assembly of claim 16, whereinthe replacement piece is a portion of a leading edge of a turbine vane.